Oral Anatomy and Occlusion - Mandibular Premolars

Mandibular First Premolars - Begin Formation

1 3/4 - 2 years

Mandibular First Premolars - Eruption

10-12 years

Mandibular First Premolars - Root Completion

12-13 years

Bell shaped crown

The "bell shape" refers to the dimensions of the crown at the contact area compared to the cervical constriction.

Mandibular First Premolar - Coronal Outline (occlusal view)

diamond

Mandibular First Premolar - Mesial Outline (occlusal view)

narrow arc
has the appearance of anterior tooth

Mandibular First Premolar - Distal Outline (occlusal view)

Broader arc
Appears more like a posterior tooth

Mandibular First Premolar - Facial and Lingual heights of contour (occlusal view)

both are MESIAL to center

Mandibular First Premolar - Facial cusp slopes (occlusal view)

cross the tooth midway F/L

divide the crown in half faciolingually.

MF cusp slope is slightly shorter than DF cusp slope.

Mandibular First Premolar - Facial and lingual cusp tips (occlusal view)

slightly M to center on the crown M/D

Mandibular First Premolar - proximal contacts

located in the middle third, almost centered buccolingually (B/L).

M contact is narrower B/L than D contact

Mandibular First Premolar - unique features

transverse ridge
occlusal pits

Mandibular First Premolar - Mesiolingual Developmental Groove

begins in the M pit on the occlusal surface and extends onto the ML surface of the crown and even onto the root.

Mandibular First Premolar - proximal contacts (buccal view)

M contact is located more cervically than the D contact

Mandibular First Premolar - location of cusp tip (buccal view)

mesial to center

Mandibular First Premolar - length of cusp slopes (buccal view)

M < D cusp slope

Mandibular First Premolar - curvature of CEJ (buccal view)

Less curve than anterior teeth

Mandibular First Premolar - taper of root (buccal view)

smoothly tapered, may curve at apex

Mandibular First Premolar - taper of crown and root (lingual view)

taper to the lingual

Mandibular First Premolar - lingual cusp (lingual view)

the lingual cusp is much shorter
much of the occlusal table is visible

Mandibular First Premolar - buccal and lingual cusp tips (lingual view)

B and L cusp tips are Mesial to center on the crown

Mandibular First Premolar - buccal cusp tip location (proximal view)

centered B/L

Mandibular First Premolar - ML developmental groove (proximal view)

on the M surface of crown and root

visible from the mesial

Mandibular First Premolar - buccal and lingual heights of contour (proximal view)

B: cervical 1/3
L: middle 1/3

Mandibular First Premolar - orientation of the occlusal table (proximal view)

tipped to the LINGUAL

note that the M marginal ridge parallels the occlusal table

Lingual tilt of Mandibular Premolar Crowns (see photo)

Mandibular Second Premolar - Formation

2 1/4 - 3 years

Mandibular Second Premolar - Eruption

11-12 years

Mandibular Second Premolar - Root Completion

13-14 years

Mandibular Second Premolars: basic traits

1) More variable in form.
2) May be formed from 4 or 5 lobes.
3) Y, H and U types with Y type being the most common.

Mandibular Second Premolars: coronal outline (Occlusal View)

cusp variant may diverge toward the lingual creating smaller lingual embrasures

Mandibular Second Premolars: facial height of contour (Occlusal View)

prominent F height

Mandibular Second Premolars: mesial and distal contact areas (Occlusal View)

broad

Mandibular Second Premolars: position of cusp tips (Occlusal View)

B cusp tip - M to center
ML cusp tip - M to center
DL cusp tip - D to center

Mandibular Second Premolars: occlusal groove pattern (Occlusal View)

3 named grooves

- mesial groove

- distal groove

- lingual groove

Mandibular Second Premolars: cusp size (Occlusal View)

B> ML> DL

* ML > DL will help you identify right and left.

U and H types (2-cusp variants)

These two types are usually formed from 4 lobes, not 5 (so: 2 cusps)

Lingual cusp located M to center

Occlusal groove pattern quite variable

Usually tapers slightly toward the lingual

Still have a large buccal cusp.

Still have broad M and D contact areas

Mandibular Second Premolars: cusp (Buccal View)

1 large cusp
cusp tip M to center

Mandibular Second Premolars: CEJ (Buccal View)

still curves but not as much as the teeth anterior to it

Mandibular Second Premolars: Root (Buccal View)

conical with apex often turned to the distal

Mandibular Second Premolars: mesial marginal ridge (Buccal View)

mesial MR is higher/more occlusal in crown than distal MR

Mandibular Second Premolars: mesial and distal contacts (Buccal View)

near the junction of the occlusal and middle thirds of the crown

Mandibular Second Premolars: ML Cusp (Lingual View)

ML cusp LARGER than DL cusp (if DL cusp is present)

Mandibular Second Premolars: CEJ (lingual view)

relatively flat

Mandibular Second Premolars: root (lingual view)

usually tapers slightly to the lingual

Mandibular Second Premolars: buccal cusp tip position (proximal view)

less lingual crown tilt

Mandibular Second Premolars: CEJ (proximal view)

CEJ is flattened

Mandibular Second Premolars: Buccal and Lingual Heights of Contour (proximal view)

B: near the junction of the cervical and middle 1/3's
L: middle 1/3

Crown tilt: mandibular 1st vs 2nd premolars (see photo)